Using extra systoles and the micro-fluid challenge to predict fluid responsiveness during cardiac surgery

Fluid responsiveness prediction is difficult during cardiac surgery. The micro-fluid challenge (micro-FC; rapid central infusion of 50 ml) and the extrasystolic method utilising post-extrasystolic preload increases may predict fluid responsiveness. Two study windows during coronary artery bypass graft surgery were defined, 1: After anaesthesia induction until surgical incision, 2: Left internal mammarian artery surgical preparation period. Each window consisted of 10-15 min observation for extrasystoles before a micro-FC was performed, after which a traditional fluid challenge (FC) was performed (5 ml/kg). Extrasystolic and micro-FC induced changes in hemodynamic variables were derived as predictors of fluid responsiveness defined as stroke volume increasing > 10% following FC. 61 patients were studied. Post-ectopic changes in pulse pressure (PP) predicted fluid responsiveness with receiver operating characteristic area (AUC) of 0.69 [CI 0.40;0.97] in the first study window and 0.64 [0.44;0.86] in the second window. Other post-ectopic predictors such as pre-ejection period (PEP) and systolic blood pressure (SBP) had similar or lower AUCs. Heart rate was 52.9 (SD ±8.4) min^- 1 and 53.6 (± 8.8) min^- 1 in the two study windows. Micro-FC induced changes in PEP had AUC of 0.74 [0.57;0.90] in the first window and 0.60 [0.40;0.76] in the second window. Correcting micro-FC induced changes in PEP for the micro-FC induced changes in heart rate had AUCs of 0.84 [0.70;0.97] in the first window and 0.63 [0.47;0.79] in the second window. The investigated methods revealed insufficient validity during cardiac surgery. RR interval corrected changes during a micro-FC should be investigated further. Trial registration Clinicaltrials.gov: NCT03002129.